You don't need expensive equipment to exercise, improve your sports skills and relieve tense muscles. With a few tennis balls and some long socks, you can practice your tennis swing and exercise the muscles of your back and neck. Using tennis balls in a sock can improve your muscles or help relieve pain.

Tennis Serve Motion

Recreational tennis players sometimes struggle with finding the best serve, and practicing the same serve over and over won't necessarily increase your power or precision. Instead, work on the overall serve motion. Fill two long socks with two tennis balls each and knot the top ends of the socks together. Place the knot in your racket hand and go through the motions of a serve, trying to establish a rhythm to keep the balls from hitting you in the back. The balls should fly behind you, up over your shoulder and around your body to the opposite leg. This helps you develop a fluid motion for your serve swing.

Building Tennis Muscles

Developing the proper rate of acceleration for your tennis racket is another valuable serve skill. Use two balls per sock in two socks, then go through the serve motion. This time, propel your arm forward and release the socks where the racket would normally hit the ball in a serve. The first few times, it's likely the socks will hit the ground not far from you. Work on releasing the socks earlier, which requires you to accelerate your serve earlier. This helps the socks fly farther, and helps you learn to gain power quickly before hitting the ball at the top of its arc in your tennis serve.

Leg Strength

Tennis balls can help you build leg strength by holding the proper form. Do a modified version of a squat by standing with your back against the wall and your legs slightly in front of you. Insert two tennis balls in a long sock and tie a knot beside the balls to hold them in place. Put the balls behind the middle of your back and bend your knees, pressing your back against the tennis balls. Use the rolling motion of the balls to help you keep your back straight and you bend your knees, never going beyond a 90-degree angle. Continue pushing back against the balls as you straighten your legs and push your body upward.

Muscle Pain

Neck and back pain caused by tense muscles often can be relieved with simple exercises. Tie two tennis balls tightly in a sock and lay on the floor. Place the balls behind your neck, moving your head from side to side. You can place the ball a little lower, where you neck meets your shoulders, and bend your knees so your feet are flat on the floor. Push your body back and forth so that the balls roll up and down the entire neck area. Put the balls under the middle of your back and push your body across them to allow the rolling motion to loosen muscles around your spine; the indentation between the balls keeps the pressure off the bone.